Condensation heat transfer and pressure drop of R134a inside microfin tubes - effect of fin height and fin angle

In this paper, the effects of fin height and fin angle on condensation heat transfer inside microfin tubes were investigated. One smooth and six microfin tubes with outer diameters of 9.52 mm were used to condense R134a at 30 degrees C and a mass flux range 157-347 kg/m(2)s. Each of the microfin tubes tested had 60 fins and a spiral angle of 18 degrees. In three of these tubes only the fin height was altered to 0.15, 0.20, or 0.25 mm. while the fin angle remained at 30 degrees. The remaining microfin tubes had altered fin angles to 40, 50, or 60 degrees, with the fin heights remaining at 0.20 mm. Experimental results showed that microfin tubes had distinct performance advantages over the smooth tube. Particularly, the microfin tube with fin height of 0.20 mm and fin angle of 50 degrees produced condensation heat transfer coefficients 215-250 per cent higher than those of the smooth tube, with average increases in pressure drops at 115-160 per cent. Four frequently cited correlations were used to predict the heat transfer coefficient for condensation inside smooth tubes. Of these correlations, the predictive method proposed by Cavallini et al. [1] that takes into account the wide range of flow patterns encountered in condensation at various mass fluxes was found to best predict the experimental results. For microfin tubes, the model by Yu and Koyama [2] predicted the experimental results with least deviation from experimental results compared to that of Cavallini et al. [3, 4] and that of Kedzierski and Goncalves [5].